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ABSTRACT: The protozoan parasite Theileria (spp. parva and annulata) infects bovine leukocytes and provokes a leukaemia-like disease in vivo. In this study, we have detected a type 1 serine/threonine phosphatase activity with phosphorylase a as a substrate, in protein extracts of parasites purified from infected B lymphocytes. In contrast to this type 1 activity, dose response experiments with okadaic acid (OA), a well characterised inhibitor of type 1 and 2A protein phosphatases, indicated that type 2A is the predominant activity detected in host B cells. Furthermore, consistent with polycation-specific activation of the type 2A phosphatase, protamine failed to activate the parasite-associated phosphorylase a phosphatase activity. Moreover, inhibition of phosphorylase a dephosphorylation by phospho-DARPP-32, a specific type 1 inhibitor, clearly demonstrated that a type 1 phosphatase is specifically associated with the parasite, while the type 2A is predominantly expressed in the host lymphocyte. Since an antibody against bovine catalytic protein phosphatase 1 (PP1) subunit only recognised the PP1 in B cells, but not in parasite extracts, we conclude that in parasites the PP1 activity is of parasitic origin. Intriguingly, since type 1 OA-sensitive phosphatase activity has been recently described in Plasmodium falciparum, we can conclude that these medically important parasites produce their one PP1.
Molecular and Biochemical Parasitology 10/2000; 110(1):161-6. · 2.55 Impact Factor
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ABSTRACT: Theileria is an intracellular parasite that causes lymphoproliferative disorders in cattle, and infection of leucocytes induces a transformed phenotype similar to tumour cells, but the mechanisms by which the parasite induces this phenotype are not understood. Here, we show that infected B lymphocytes display constitutive phosphoinositide 3-kinase (PI3-K) activity, which appears to be necessary for proliferation, but not survival. Importantly, we demonstrate that one mechanism by which PI3-K mediates the proliferation of infected B lymphocytes is through the induction of a granulocyte-monocyte colony-stimulating factor (GM-CSF)-dependent autocrine loop. PI3-K induction of GM-CSF appears to be at the transcriptional level and, consistently, we demonstrate that PI3-K is also involved in the constitutive induction of AP-1 and NF-kappaB, which characterizes Theileria-infected leucocytes. Taken together, our results highlight a novel strategy exploited by the intracellular parasite Theileria to induce continued proliferation of its host leucocyte.
Cellular Microbiology 09/2000; 2(4):329-39. · 5.46 Impact Factor
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ABSTRACT: Cells use phosphorylation/dephosphorylation mechanisms to regulate the activity of several proteins required to transmit information from the cell surface to the nucleus. Recent studies have significantly increased our knowledge regarding the structure/function of one major regulator of cell phosphorylation: protein phosphatase 2A (PP2A). This review will discuss the role of PP2A in virology and parasitology.
Microbes and Infection 05/2000; 2(4):401-7. · 3.10 Impact Factor
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ABSTRACT: The transcription factor Sp1 regulates the activity of a large number of eukaryotic gene promoters, including early SV40 and human immunodeficiency virus type 1 (HIV-1). Here, we report that expression of SV40 small tumor antigen (small t) in quiescent CV-1 cells transactivates two Sp1-responsive promoters, including a deletion mutant of HIV-1 LTR, through specific inhibition of endogenous AC and ABalphaC forms of protein phosphatase 2A (PP2A). Expression of a small t mutant, lacking the PP2A-binding domain, failed to transactivate Sp1. Overexpression of the B56alpha, B56beta, and B56gamma1 regulatory PP2A subunits strongly inhibited the ability of small t, but not the phosphatase inhibitor, okadaic acid, to enhance Sp1-driven gene expression. Using inhibitors and co-expression of kinase-deficient mutants, we also show that functional phosphatidylinositol 3-kinase (PI 3-kinase) and atypical protein kinase C zeta are required for small t-induced Sp1-dependent promoter transcriptional activation. Moreover, two inhibitors of PI 3-kinase, wortmannin and LY294002, inhibit the initiation of SV40 DNA replication in quiescent CV-1 cells. Taken together, these results suggest that PP2A and PI 3-kinase contribute to the ability of small t to regulate Sp1 activity, stimulate early SV40 DNA replication, and enhance the transformation of resting cells during SV40 infection.
Journal of Biological Chemistry 04/2000; 275(13):9385-9. · 4.77 Impact Factor
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Parasitology Today 04/1999; 15(3):90-2.
